It is LinkedIn’s tool for segmenting people, and it is really powerful. You can segment on:
Geography
Relationship (1st, 2nd or 3rd connection)
Industry
Profile languages
Seniority (owner, ceo, all the way to entry position)
Years at current company
Years in current position
The company size (headcount)
Company type.
(And more…)

So you could say to LinkedIn:
Give me every single person in the united states with gym owner as their position and have worked as that for less than a year.

Now this is the cool part, if the search returns 1000 people or less you can import them into a software called anyleads.

So you can use these different segmentations on your target group to export them all.

If they have an email on their profile you’ll get that. As far as I’ve seen you’ll get emails on anywhere between 30% and 60% of leads.